Factors influencing the clinical performance of x-ray systems both dental and medical are being modeled and evaluated in vitro using computer simulations and quantitative measurements derived from radiographic phantoms. The effects of continuous probability density functions on diagnostic systems are being explored theoretically using a Bayesian approach. When applied to quantum-limited x-ray systems it is possible to express information transfer vs. x-ray modulation and photon fluence for a variety of radiographic systems of biomedical interest. Of particular concern is the relative influence of continuous measures of prior information. The effect of extraneous x-ray scatter on photon statistics and radiographic contrast has been assessed as has been the role played by variations in spectral sensitivity and nonlinear contrast gain associated with common film-screen systems. Comparable work on non-screen film systems largely has been completed which confirms previous statements regarding the projected impact of exposure reduction on diagnostic performance.